Thermo-plastic laminated structure

ABSTRACT

A thermo-plastic laminated structure, a production method, and an application thereof characterized in that a plurality of thermo-plastic sheets, inclusive of a foamed plastic sheet, are bonded together employing solvent evaporation type adhesive into a laminated structure which is thereafter provided with a plurality of minute holes bored mechanically in the direction of the thickness of the structure under the following limitations: 1. The holes thus bored reach the adhesive layer interposed between the component plastic sheets, whereby one or both sides of said adhesive layer are communicated with the outside atmosphere through said plurality of holes; and 2. The holes, however, do not penetrate the thermoplastic structure totally, whereby both sides of the thermoplastic structure are not communicated each other through these plurality of holes. The structure is thereafter subjected to a curing process and vacuum formed into for instance a vibration plate of a loudspeaker.

D United States Patent 1151 3,674,109 Murase 1 1 July 4, 1972 1541THERMO-PLASTIC LAMINATED 3,229,785 1/1966 P0113511 ..161/113 x STRUCTURE3,285,364 1l/1966 Cohen... 3,396,062 8 1968 Wh't ..264 [72] Inventor:Yoshlhiko Murase, llamamatsu, Japan 1 l e [321 [73] Assignee: NipponGaltlti Seizo Kabushiki Kaisha, FOREIGN PATENTS OR APPLICATIONSHamamatswshi. Japa 362,521 7/1962 Switzerland ..156/87 [22] Filed:Primary Examiner-Robert F. Burnett [21] Appl. No.1 65,204 AssistantExaminer-Joseph C. Gil

Attorney-Lemer, David 81. Littenberg D [30] Foreign App lcation Priorityata ABSTRACT 23:: 4 2 A thermo-plastic laminated structure, a productionmethod, Aug. 1969 Japan "44/6691! and an application thereofcharacterized in that a plurality of thermo-plastic sheets, inclusive ofa foamed plastic sheet, are 52 us. or. ..1s1/32 R, 156/87, 156/253bonded mgethe P' 50mm evapmlion W adhesive 156/285. 156/286, 161/113,161/125, 161/159: into a laminated structure which is thereafterprovided with a 0 plurality of minute holes bored mechanically in thedirection [5|] [nL 1 325 00 1332 3110 101 13 00 of the thickness of thestructure under the following limita- [58] Field of Search..161/112,113, 125; 156/87,

156/253, 285, 286; 181/31 R, 31 B, 32 R, 63 1. The holes thus boredreach the adhesive layer interposed between the component plasticsheets, whereby one or 56 References Cit d both sides of said adhesivelayer are communicated with the outside atmosphere through saidplurality of holes; UNITED STATES PATENTS and 2. The holes, however, donot penetrate the thermoplastic l :gwz structure totally, whereby bothsides of the thermoplastic 2'36 M944 sgfl' 12 x structure are notcommunicated each other through these 2,605,204 7/1952 Benedict et a1.161 1 13 x 9 5/1954 cIark l6l/l X The structure is thereafter subjectedto a curing process and 2.306.812 9/l957 X vacuum formed into forinstance a vibration plate of a loud- 2,850,423 9/1958 Kramp et al.161/113 X speaker 2,905,260 9/1959 Wi1liams........ ..181/32 2,978,3764/1961 l-lulse ..161/1 13 X 1 Claim, 8 Drawing Figures PATENTEnJum m23.674.109

sum 1 or g 15:55:5 1 1 11,-, It r111 01 It l/IIIIIIIIIIII II II II III,1

' II IIIIIIIII II II I! g PATENTEDJUL' 4 we saw 2 or 2 FIG.8

FIG.7

THERMOPLASTIC LAWNATED STRUCTURE BACKGROUND OF THE INVENTION Thisinvention relates to thermo-plastic laminated structures wherein two ormore of thermo-plastic sheets are laminated together employing a solventevaporation type adhesive (bonding agent). The invention furthermorerelates to a production method of the above mentioned structures andtheir application.

Heretofore, when it is desired to produce a multi-layer structure ofthermo-plastic sheets inclusive of a foamed plastic sheet of forinstance polystyrene, the component layers of the above describedstructure have been bonded together employing adhesive of solvent type.However, since the conventional construction of the thermo-plasticsheets has afforded scarcely any gas permeability and also the foamedplastic sheet has possessed a comparatively heavy thickness havingseparately dispersed foams (closed cellules) therein, evaporation of thesolvent of the adhesive has taken a long period of time and theproduction efficiency thereof has been reduced. Furthermore, there hasbeen a much possibility of the solvent vapor or air being seized betweenthe bonded layers to create bubbles therein thus causing swellings orwrinkles on the surface of the laminated structure while the laminatedsheets undergo subsequent processes such as hot press and vacuumforming. This causes an occurrence rate of water products at a highlevel elevating the production cost for each products.

SUMMARY OF THE INVENTION Therefore, a primary object of this inventionis to eliminate the above mentioned shortcomings of the conventionallaminated structure of plastic sheets.

Another object of the present invention is to provide an improvedconstruction of the laminated structure wherein remaining solvent gas orvapor of the bonding agent or air between the laminated sheets, andhence the possibility of causing swellings or wrinkles on the surface ofthe laminated structure, is completely eliminated.

Still another object of the invention is to provide an improvedconstruction of the laminated structure consisting of thermo-plasticcomponent sheets bonded together by means of a bonding agent of solventtype, wherein the bonding layer is communicated with the outsideatmosphere through one or both sides thereof, so that the vapor or gasof the solvent or air does not stay in the bonding layer but is quicklydispersed into the atmosphere, whereby the lamination treatment andshaping process following thereafter are much facilitated.

Still another object of the invention is to provide an improvedconstruction of the laminated structure consisting of thermo-plasticcomponent sheets bonded together employing a bonding agent, wherein thebonding layer is communicated to the outside atmosphere through a plentyof holes bored through one or both sides component sheets, so that anygas or air staying in the bonding layer is quickly dispersed into theatmosphere, whereby the creation of swellings or wrinkles on the surfaceof the laminated structure is substantially eliminated.

A further object of the invention is to provide an improved constructionof the thermoplastic laminated structure having a plenty of holes on oneor both side surfaces thereof, but yet maintaining a gas impermeablenature through the inhole thickness of the laminated structure, wherebythe structure may be thereafter formed through a vacuum forming process.

A still further object of the invention is to provide an improved methodfor producing the thermo-plastic structure of the above describedconstruction.

An additional object of the invention is to provide an application ofthe thermo-plastic structure of the above described construction.

These and other objects of the invention can be achieved by an improvedconstruction of a thermo-plastic structure which comprises two or moresheets of thennoplastic material, inclusive of a foamed plastic sheetbonded together by adhesive (bonding agent) into a laminated structure,one or both sides of said structure having a plurality of minute holesbored under the following limitations:

1. The holes reach the bonding agent layer interposed between thecomponent plastic sheets, whereby one or both sides of said bondingagent layer are communicated with the outside atmosphere in thedirection of the thickness (i.e., direction perpendicular to the plane)of the thermo-plastic structure; and yet,

2. the holes do not penetrate the thermo-plastic structure completely inthe direction of the thickness of the structure, whereby both sides ofthe therrno-plastic structure are not placed under a directlycommunicated condition.

According to another aspect of the invention, there is provided animproved method for producing the thermo-plastic structure of the abovedescribed construction, which comprises the manufacturing steps ofapplying a bonding agent on the bonding surfaces of thermo-plasticsheets inclusive of a foamed plastic sheet, laminating a plurality ofsuch sheets into a multi-layer construction, boring a plurality of holeson one or both side surfaces of the thus laminated construction underfollowing limitations:

1. The holes reach the bonding agent layer interposed between thecomponent plastic sheets, whereby one or both sides of said bondingagent layer are communicated with the outside atmosphere in thedirection of the thickness of the thermo-plastic structure; and yet,

2. The holes do not penetrate the thermo-plastic structure completely inthe direction of the thickness of the structure, whereby both sides ofthe thermo-plastic structure are not placed under a directlycommunicated condition, and curing the bonding agent layer after theplurality of holes are bored mechanically in the direction of thethickness of the laminated structure.

According to still another aspect of the present invention, there isprovided an improved vibration plate for a loudspeaker constituting anapplication of the thermo-plastic structure according to the firstaspect of the invention, wherein a thermo-plastic sheet is bonded on thesurface of a foamed sheet of a synthetic resin through an interposedbonding agent layer and a flat portion is integrally formed around thecone of the speaker, characterized in that a plenty of minute holes areprovided on said flat portion of the speaker in a manner that the minuteholes are spaced apart each other by a predetermined distance and boredfrom the upper surface of the thermoplastic sheet to reach the bondingagent layer.

The invention will be better understood from the following descriptionwhen read in conjunction with the accompanying drawings wherein likeparts are designated by like reference numerals and characters.

BRIEF DESCRIPTION OF DRAWINGS In the drawings:

FIG. 1 is a cross-sectional view, in a much enlarged scale, of anexample of the thenno-plastic laminated structure according to thepresent invention;

FIG. 2 is a cross-sectional view, in a much enlarged scale, of a secondexample of die thermo-plastic laminated structure according to theinvention;

FIGS. 3 through 6 are cross-sectional views also enlarged and showingproduction steps of the thermo-plastic structure, which constituteanother aspect of the present invention;

FIG. 7 is a front view showing a vibration plate for a loud speakerwhich constitutes one application of the thermoplastic laminatedstructure according to this invention; and

FIG. 8 is a crosssectional view, in much an enlarged scale, taken alongthe line VIII VIII in FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1 showing anexample of the thermoplastic laminated structure according to thepresent invention, it is clearly indicated that the laminated structurecomprises a basic sheet I consisting of, for instance, polystyrene paper(foamed polystyrene sheet) and a polyvinyl chloride resin sheet 3overlying the basic sheet 1 through an interrnediately disposed layer 2of solvent evaporation type adhesive including organic solvent type;aqueous solution type and emulsion type, for instance, vinyl acetatefamily. In the overlying layer 3 made of a polyvinyl chloride resin, anumber of minute holes 4, 4, 4, are bored at positions regularlyarranged thereon and in a direction along the thickness (i.e.,perpendicular to the plane) of the laminated structure so that the holesreach the intermediate layer 2 consisting of the above mentioned vinylacetate type adhesive.

Because of the existence of the minute holes, the drying and curingsteps of the adhesive (bonding agent) layer are accelerated. That is,the solvent (i.e., organic solvent and water) of the bonding agent isevaporated through these holes into the outside atmosphere, and thecreation of bubbles or a part of air seized therein during thelaminating step of the basic sheet and the overlying sheet is therebyprevented. As a result, the possibility of fon'ning swelled portions orwrinkles on the surface of the laminated structure during the subsequentcuring and forming steps (generally applying heat) of the structure iscompletely eliminated.

Referring to FIG. 2 showing another example of the thermoplasticlaminated structure according to the invention, there is indicated thatthe example of the structure comprises a basic sheet made of polystyrenepaper 1, a polyvinyl chloride sheet 3 overlying the upper surface of thebasic sheet 1, and an ABS (acrylonitrilebutadiene-styrene) resin sheet 5underlying the basic sheet 1. These three sheets are bonded togetherinto a three layer structure through bonding agent layers 2 and 2aconsisting of a bonding agent of, for instance, vinyl acetate type.Accordingly to the characteristic feature of this invention, the uppersheet 3 is bored with a plurality of minute holes 4, 4, 4, and the lowersheet 5 and the basic sheet 1 inclusive of the bonding layer are boredwith a plurality of minute holes 6, 6, 6, so that the both kinds of theminute holes reach the upper and lower surfaces of the bonding agentlayer 2, respectively At this point, it should be noted that the minuteholes 4, 4, 4, and another set of minute holes 6, 6, 6, are bored atpositions staggered or offset between each other, so that there is nopossibility of anyone of the upper holes 4, 4, communicates with anyoneof the lower holes 6, 6, 6, (in this case, the bonding agent layer 2 isacting as a barrier between the two sets of holes).

With the above described construction of the thermoplastic laminatedstructure, the bonding agent layer 2 is evaporated and cured, throughthe minute holes 4, 4, 4, and the bonding agent layer 20 is evaporatedand cured through the minute holes 6, 6, 6, The bonding agent layer 2 isfurthermore partly dried out through the minute holes 6, 6, 6, wherebythe evaporation and the curing of these bonding layers 2 and 2a areaccelerated.

It will be apparent that the provision of the minute holes may becarried out mechanically along the direction of the thickness of thelaminated structure, and through these holes any air or gas seizedbetween the laminated sheets during the bonding step can be dispersedinto the outside atmosphere.

For both of the above described reasons, the required time period in thedrying and curing step of the laminated structure can be substantiallyshortened, and swellings or wrinkles caused in the subsequent steps mayalso be eliminated. Furthermore, since the holes do not penetrate thecomplete thickness of the laminated structure, or because the holesbored at one side surface of the structure do not communicate with otherholes bored at the other side of the structure, the structure is madesubstantially non-permeable for air or gas, and the structure can beformed thereafter into various required shapes by way of the vacuumforming process.

Referring to FIGS. 3 through 6, there are indicated sequential stepsemployed for the production of a loudspeaker diaphragm utilizing thethermo-plastic laminated structure, which constitutes a second aspect ofthe present invention. In-

itially, there are prepared, as shown in FIG. 3 a basic sheet I made of,for instance, polystyrene paper and a polyvinyl chloride sheet 3, botharranged to be in an overlying relation one on the other. Then these twosheets 1 and 3 are laminated together as shown in FIG. 4 after theapplication of adhesive of organic solvent type on either one of theconfronting surfaces of the sheets 1 and 3. As described before, whenthese two sheets are bonded together, there is a tendency of causingseizure of air or gas between the confronting surfaces of the sheets 1and 3 in which the adhesive is applied. For eliminating this tendency,the construction of the thenno-plastic structure according to the firstaspect of the invention is provided with a plenty of minute holes in oneor both side surfaces of the structure. However, in what stage of theproduction process these holes are to be bored is a problem. If theholes are bored before the application of the adhesive, the adhesivesubsequently applied would intrude into these holes and clog theseholes.

For this reason, according to the characteristic feature of the secondaspect of the invention, the laminated structure is provided with theplurality of holes at a stage a certain time after the adhering stepindicated in FIG. 4, by means of, for instance, a needle roller 7 asshown in FIG. 5. By this way, the bonded sheets S which have been shownin FIG. 4 are now provided, as shown in FIG. 5, with the plurality ofholes 4, 4, 4, extended along the direction of the thickness of thestructure S through the polyvinyl chloride sheet 3 in a mechanicalmanner until the holes reach the adhesive layer 2 interposed between thetwo layers 1 and 3. Since the plurality of holes 4, 4, 4, satisfyfollowing limitations:

1. The holes reach the adhesive (bonding agent) layer interposed betweenthe component plastic sheets, whereby one or both sides of the bondingagent layer are communicated with the outside atmosphere in thedirection of the thickness of the thermo-plastic structure; and yet,

2. the holes do not penetrate the thermo-plastic structure completely inthe direction of the thickness of the structure, whereby both sides ofthe thermo-plastic structure are not placed under a directlycommunicated condition, any air or gas or vapor of the solvent of thebonding agent can be delivered into the outside atmosphere through theseholes, and lastly the bonded structure S with the bonding agent thusdried out and cured is subjected to the subsequent forming step, such asa vacuum forming step, so that a formed product P as a loudspeakerdiaphragm indicated in FIG. 6 is obtained.

In FIGS. 7 and 8, a loudspeaker which constitutes another preferredexample of the present invention is illustrated.

Heretofore, various attempts have been done to produce the diaphragm orvibration plate of a loudspeaker employing a foamed synthetic resin basesheet made of, for instance, polystyrene paper overlaid by athermo-plastic sheet of, for instance, polyvinyl chloride with theinterposition of an adhesive layer of emulsion type polyvinyl acetatefamily therebetween. However, because of these sheets having scarcelyany air or gas permeability, there has existed a tendency of some partof gas or vapor of the solvent (water) of the adhesive staying in thelayer between the two sheets or air being seized in the same layer dueto careless treatment in the bonding process, whereby swellings orwrinkles may be created on the surface of the resultant laminatedstructure as described before, and this may effect deleteriously on tonecolor of the output sound or frequency characteristics of theloudspeaker.

The above described shortcomings of the conventional diaphragm orvibration plate can be eliminated completely by the employment of animproved construction according to the present invention. As shown inFIGS. 7 and 8, the improved construction of the vibration plate of aloud-speaker comprises a foamed synthetic resin base sheet I made of,for instance, polystyrene paper and a thermo-plastic sheet 3 made of,for instance, polyvinyl chloride, both sheets being bonded togetherthrough the use of adhesive 2 of emulsion type vinyl acetate family.

The manufacturing steps of this embodiment is almost same as abovementioned steps relating to FIGS. 3 to 6, except that this embodiment isso arranged that the last forming step can be carried out before thecomplete curing of the adhesive layer in the laminated construction,thereby shortening the manufacturing time. Firstly, the base sheet 1 andthe thermoplastic sheet 3 are bonded together using adhesive 2 by thesame process as shown in FIG. 4. Two sheets 1 and 3 thus bonded togetherare thereafter subjected to hot-press for initiatin g curing, andaccording to a characteristic feature of this invention, the thustreated structure is provided with numerous holes 4,4, 4, distributedonly on the surface of the region which will later become a flat portion8 surrounding the cone portion 9 of the vibration plate and at positionsspaced apart between each other by a desired distance in such a mannerthat the holes are bored from the upper surface of the polyvinylchloride sheet 3 until they reach the adhesive layer 2 interposedbetween the base sheet 1 and the polyvinyl chloride sheet 3. Thediameter of the holes 4, 4, 4, may be selected to a suitable valuebetween about 0.1 and 1.0 mm, and the distance between each holes may beselected to about 2 cm.

The central region which will later become the conical portion 4 is leftunbored, but the effect of this invention can be substantiallyaccomplished, as the area of this portion is only a fraction of thewhole diaphragm area. As this portion is not provided with holes on thesheet 3, the vacuum suction forming can be applied before the completecuring of adhesive layer 2 without causing the parting-off of the twosheets 1 and 3, whereby the manufacturing time is substantially reduced.Otherwise, air would go through the holes into the adhesive layer 2,resulting in that only the base sheet 3 would be subjected to thesuction and the thermo-plastic sheet 1 would not closely follow the basesheet 3.

The above described boring step of the numerous holes 4, 4, 4, may alsobe exercised prior to the hot-press application. However, in such acase, the uncured adhesive may intrude into the holes thus bored andclog these holes, reducing the advantageous feature of these holessubstantially.

Of course, the above described holes may be bored alternatively throughthe base sheet 1 made of polystyrene paper, and in diis case, the meritof the holes stays unchanged.

With the above described construction of the vibration plate of aloudspeaker, swellings, wrinkles, and defonnation caused in the case ofthe conventional structures can be completely eliminated, whereby soundsof far beautiful tonecolor and of better fidelity in frequency responsecan be reproduced from the loudspeaker employing the vibration plate.

Although the invention has been described with respect to preferredembodiments thereof, it will be apparent to those skilled in the artthat various modifications and alterations may also be carried outwithout departing the spirit and scope of the present invention, andthese are all included in the scope of the present invention as definedhereinbelow.

Iclaim:

l. A vibration plate for a loudspeaker comprising a laminate structureincluding a foamed synthetic resin sheet and a thermo-plastic resinsheet bonded thereon by a bonding agent layer interposed therebetween,said laminate structure having a centrally located cone portion and aflat portion surrounding the cone portion, and further including aplurality of minute holes provided only on said flat portion of saidlaminate structure, and not on said cone portion, said holes spacedapart from each other by a predetermined distance, said holes extendingfrom the upper surface of said thermo-plastic resin sheet to saidbonding agent layer.

1. A vibration plate for a loudspeaker comprising a laminate structureincluding a foamed synthetic resin sheet and a thermoplastic resin sheetbonded thereon by a bonding agent layer interposed therebetween, saidlaminate structure having a centrally located cone portion and a flatportion surrounding the cone portion, and further including a pluralityof minute holes provided only on said flat portion of said laminatestructure, and not on said cone portion, said holes spaced apart fromeach other by a predetermined distance, said holes extending from theupper surface of said thermo-plastic resin sheet to said bonding agentlayer.